In high power digital architectures, the demodulated received signal is often found to be a good representation of the binary or M-ary code that was originally transmitted given that channel perturbations are small with regard to signal parameters. Such a demodulated signal, as shown in FIG. 1, represents an ideal signal which has relatively constant minimum and maximum peaks about a relatively constant threshold level. Such a signal may easily be converted into ones and zeroes through the use of hard limiters.
However in low power radio architectures that are presently required in wireless applications, the transmitted signals have low amplitudes and/or low FSK/PSK deviations for low bandwidths; therefore when detected are found to experience degradations from noise and such as Rayleigh/Ricean fading where the maximum and minimum peaks are far from constant. In addition, the frequency offsets between the transmitter and receiver, and the dc offsets in the circuitry will change the mean value of the demodulation level. In the case where a fixed threshold is used to determine the bit values, it may occur that some minimum peaks are above the threshold or some maximum peaks are below the threshold resulting in bit errors. One solution used in such cases is to generate a dynamic threshold which is calculated to be midway between a sequential maximum and minimum as illustrated in FIG. 2. Though this type of solution has merit for the detection of binary signals, high bit error rates (BER) can still occur when detecting M-ary signals.
Therefore there is a need for quickly and dynamically generating decision thresholds that can effectively be used to decode signals having multiple levels.